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Internet Engineering Task Force (IETF) S. Sorce
Request for Comments: 8732 H. Kario
Updates: 4462 Red Hat, Inc.
Category: Standards Track February 2020
ISSN: 2070-1721
Generic Security Service Application Program Interface (GSS-API) Key
Exchange with SHA-2
Abstract
This document specifies additions and amendments to RFC 4462. It
defines a new key exchange method that uses SHA-2 for integrity and
deprecates weak Diffie-Hellman (DH) groups. The purpose of this
specification is to modernize the cryptographic primitives used by
Generic Security Service (GSS) key exchanges.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8732.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction
2. Rationale
3. Document Conventions
4. New Diffie-Hellman Key Exchange Methods
5. New Elliptic Curve Diffie-Hellman Key Exchange Methods
5.1. Generic GSS-API Key Exchange with ECDH
5.2. ECDH Key Exchange Methods
6. Deprecated Algorithms
7. IANA Considerations
8. Security Considerations
8.1. New Finite Field DH Mechanisms
8.2. New Elliptic Curve DH Mechanisms
8.3. GSS-API Delegation
9. References
9.1. Normative References
9.2. Informative References
Authors' Addresses
1. Introduction
Secure Shell (SSH) Generic Security Service Application Program
Interface (GSS-API) methods [RFC4462] allow the use of GSS-API
[RFC2743] for authentication and key exchange in SSH. [RFC4462]
defines three exchange methods all based on DH groups and SHA-1.
This document updates [RFC4462] with new methods intended to support
environments that desire to use the SHA-2 cryptographic hash
functions.
2. Rationale
Due to security concerns with SHA-1 [RFC6194] and with modular
exponentiation (MODP) groups with less than 2048 bits
[NIST-SP-800-131Ar2], we propose the use of hashes based on SHA-2
[RFC6234] with DH group14, group15, group16, group17, and group18
[RFC3526]. Additionally, we add support for key exchange based on
Elliptic Curve Diffie-Hellman with the NIST P-256, P-384, and P-521
[SEC2v2], as well as the X25519 and X448 [RFC7748] curves. Following
the practice of [RFC8268], only SHA-256 and SHA-512 hashes are used
for DH groups. For NIST curves, the same curve-to-hashing algorithm
pairing used in [RFC5656] is adopted for consistency.
3. Document Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
4. New Diffie-Hellman Key Exchange Methods
This document adopts the same naming convention defined in [RFC4462]
to define families of methods that cover any GSS-API mechanism used
with a specific Diffie-Hellman group and SHA-2 hash combination.
+--------------------------+--------------------------------+
| Key Exchange Method Name | Implementation Recommendations |
+==========================+================================+
| gss-group14-sha256-* | SHOULD/RECOMMENDED |
+--------------------------+--------------------------------+
| gss-group15-sha512-* | MAY/OPTIONAL |
+--------------------------+--------------------------------+
| gss-group16-sha512-* | SHOULD/RECOMMENDED |
+--------------------------+--------------------------------+
| gss-group17-sha512-* | MAY/OPTIONAL |